1. Field of the Invention
This invention concerns the treatment of water to remove therefrom inorganic ions, and more particularly relates to a method and apparatus for such treatment which permits an existing water flow at a given location to facilitate such treatment.
2. Description of the Prior Art
Water treatment installations for removing impurities from water are well known. For example, most cities or municipalities have a water purification plant wherein incoming water is treated by various filtration steps to remove suspended matter, and is eventually treated with a oxidizing agent such as chlorine or ozone which destroys dissolved organic species. A certain percentage of dissolved inorganic species become bound to the suspended matter which is removed by filtration. Larger amounts of dissolved metals can be removed by addition of compounds of
iron or aluminum, which form a precipitate or floc structure capable of absorbing inorganic species. The precipitate or floc structure is then removed by filtration.
Such water purification installations involve considerable capital investment, and further involve high operational costs attributable to wages for operating personnel, chemicals, electricity, maintenance, and removal of sludges produced in the filtration steps. Such large water treatment facilities obviously are suitable only for municipalities or large industrial installations involving large daily volumes of water and where the high costs are affordable.
Many water pollution problems exist where the volume of water involved is so small or sporadic as not to justify remediation by way of costly facilities. Such low or sporadic flow situations are typical of ground water, storm water, landfill leachate and industrial effluents. In such situations, movement of water is generally resultant from gravity effect alone.
In many situations it is desired to selectively remove toxic inorganic ions present at small concentration amidst massive amounts of commonly abundant innocuous species. For example, in a typical groundwater situation, the water may contain great amounts of Na.sup.+, K.sup.+, Ca.sup.++, Mg.sup.++, Al.sup.+++, Cl.sup.-, and SO.sub.4.sup.--, which are all relatively harmless, and trace amounts of toxic species such as Cd.sup.++, Pb.sup.++, Cr.sup.+++, Hg.sup.++, Ag.sup.+, AsO.sub.4.sup.-3 and CrO.sub.4.sup.-2. Prior methods for removing dissolved inorganic ions from water include: distillation, reverse osmosis, addition of precipitating ions followed by filtration, and ion exchange methods. All the aforesaid methods involve considerable capital investment and operational costs, and are not selective for toxic ions. The consequence of non-selectivity is that extensive costs are incurred in removing species that do not have to be removed.
The use of chelating resins is well known for the selective absorption of multi-valent transition heavy metals from aqueous solutions having large concentrations of other ions. However, such resins are generally manufactured in the form of spherical beads of 20-100 mesh size which must be confined within pressurized vessels. The beads present significant impedance to flow. Accordingly, the water to be treated must be pumped at high pressure through the bed of beads in the vessel. Because the chelating resins are of high cost, they must be regenerated for subsequent use. This requires specialized features of equipment and associated operating expenses. A further problem in employing a bed of small beads confined within a vessel is that, suspended matter in the ingoing water to be treated filters out within to the bed of beads to produce a clogging or binding effect that restricts further flow through the bed.
The desirability of so-called passive or in-situ water remediation techniques has received considerable attention in recent years. In such techniques, for example, groundwater would be treated without pumping it to the surface. Similarly, landfill leachates, storm water and industrial effluents would desirably be remediated in ways which would not require pumping or the intervention of equipment requiring operational personnel. A classic example of passive water remediation is the long known underground septic tank for microbial treatment of waste water effluent from residential buildings. Passive remediation systems are highly desirable at remote locations where there is no electricity and no operating personnel.
It is accordingly an object of the present invention to provide a passive water treatment method for removing dissolved inorganic ions.
It is a further object of this invention to provide a method as in the foregoing object which is substantially unaffected by the presence of suspended matter in the water undergoing treatment.
It is another object of the present invention to provide a method of the aforesaid nature wherein said inorganic ions are selectively removed from water having large quantities of other species.
It is a still further object of this invention to provide apparatus useful in carrying out the aforesaid process.
It is yet another object of the present invention to provide apparatus of the aforesaid nature which is easy to utilize, provides little impedance to flow, and is amenable to low cost manufacture.
These and other beneficial objects and advantages will be apparent from the following description.